Circad Solves Customer EMC Compliance Issues
Posted on 13th May 2015
A referred customer was suffering continuing problems with power supply failure and an inability to pass the Electrostatic Discharge tests (ESD tests) within Electromagnetic Compliance, compounded by supplier interface issues.
Their PCB assembly company had modified the layout of the power supply and the designers were blaming the power supply failure on this modification. The designers wanted to diagnose the cause of failure by attending the Electromagnetic Compliance tests at a cost of several thousands of pounds.
This customer wanted fixes not excuses or exploitation so we were invited to review the PCB schematics. Following a rapid pcb design review, we were instantly able to suggest fixes to resolve the ESD tests and field failures. We also identified other areas of the design that could be improved and predicted the failure modes if these design changes were not implemented.
We identified more inherent issues than any other supplier, and because one of these predicted failures actually happened a week later we won the business.
We manufacture and maintain a wide range of different electronic designs so we were able to look at the problem from many different angles and arrive at a reasonable opinion of the design elements that work and those which are at high risk of failure or unreliability.
We undertook a full design review and included lots of test and measurement to verify the performance of the product; we found the power transistors reached more than 100 degrees Celsius within 5 minutes of operation; they soon thereafter reach 150 degrees and fail.
We examined the PCB schematic to work out corrective action including component choice and rework to ensure the design would perform to specification. The power supply was re-tested beyond design capacity and supplied to the customer for sign off with full ISO13485 documentation.
Although the customer was pleased with the result since this achieved the design specification, it was still inherently inadequate and our proposal for a complete re-design of the power supply was accepted. The re-designed power supply only reached 17 degrees above ambient and is now in production.
Another failure was loss of communications during ESD tests. We discovered high speed differential signals were being sent across two PCB's through two sets of connectors. We recommended a modification to the signal routing that allowed the system to achieve certification through the ESD phase of full Electromagnetic Compliance testing.
We measured the system for conducted and radiated emissions using our spectrum analyser. Above is a screen shot showing a valid FSK signal transmission at 868 MHz.
We provided the customer with the EMC pre-compliance test results giving them confidence to book the product into full Electromagnetic Compliance test, passing it first time.
EMC test houses are busy, and finding a test slot for your product can take weeks. The last thing you want to fail because of a design issue within the first couple of hours of EMC test. Design issues require identifying, fixing then reworking before you can reschedule a new test slot.
Tagged as: pcb design review
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